Study On Nonlinear Characteristics And Anode Uniformity Performance Under Geomagnetic Field Effect Of Photomultiplier Tube

Cosmic rays are extremely rare substances in the universe and an important source of information for understanding the universe.As one of the core components of the cosmic ray detector,the photomultiplier tube has always been the focus of research in this field.Many high-energy cosmic ray observation devices use photomultiplier tube as detectors,and a large number of photomultiplier tube are used to detect cosmic rays in the Large High Altitude Air Shower Observatory(LHAASO)located in Ganzi Autonomous Prefecture,Sichuan Province,China.The output charge of a photomultiplier tube working under ideal conditions should be proportional to the incident light intensity.However,in practical use,with the increase of the incident light intensity,the output charge will often shift,that is,the output nonlinear phenomenon will occur.For the photomultiplier tube used in LHAASO,due to its large size,it cannot be simplified into a particle.It will receive incident light from all directions and angles in its work,and the signals generated by different incident light are often inconsistent.In order to restore the incident light information and accurately reconstruct the particle events through the photomultiplier tube output signal,it is necessary to calibrate the nonlinearity of the photomultiplier tube and the consistency of different positions.For this reason,this topic adopts the self-developed continuous neutral Optical attenuator,designs a test method to calibrate the nonlinearity of photomultiplier tube by accurately adjusting the incident light intensity,and verifies the accuracy of the test method by comparing the traditional “double light source method” test,which solves the problem of insufficient test accuracy of the “double light source method” in the area with high nonlinearity and large data files generated by the test.By precisely adjusting the incident light intensity,this topic also designed a test method for consistency scanning of large size photomultiplier tube under different incident light intensities in geomagnetic conditions and magnetic shielding conditions using a mechanical device that can be automatically programmed and controlled through a computer system,and used this method to scan the 20 inch microchannel plate multiplier structure photomultiplier tube used in LHAASO-WCDA.The test results show that the anode output uniformity of large size photomultiplier tube is low in the geomagnetic environment,and the anode uniformity is significantly improved after adding magnetic shielding.This method has high accuracy and fast testing speed,which is suitable for mass testing.It provides a new idea and solution for parameter calibration of large size photomultiplier tube.